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Monday, September 10, 2012

The NFL & LNT

The NFL is the National Football League, and LNT is the Linear, No Threshold theory of cancer induction from ionizing radiation.

There are some folks who just can't accept LNT. They typically imagine a threshold (because some epidemiological studies can't show a statistically significant increase of cancer at low doses) or that radiation is good for you (because some studies of nuclear workers show less cancer incidence than the general public).

I'll try to tackle (HA!) these misperceptions using the NFL.

This is just a broad analogy, so please no nit-picking.

A recent study has found a higher risk of neurodegenerative mortality (ndm) among football players compared with the average population. The study has its weaknesses, but my point isn't to criticize the study, it's just to show how the underlying thinking is similar to LNT. LNT isn't some unique, diabolical plot imposed on people using radioactive materials.

The NFL study also found that those players in "speed" positions had a higher mortality rate than those people in non-speed positions.

Those findings parallel the energy range of ionizing radiation and the risk of cancer. In football, below some level of kinetic energy (like if people walked rather than ran and rather than tackle, they touched) there would be no expectation of any excess ndm. There would be an energy threshold. With radiation, below a certain energy, we don't see nor expect cancer. But above that energy threshold (called "ionizing radiation"), we expect more cancer with more dose. Just like we expect a higher risk of ndm the longer someone plays professional football. The position (speed or not) is like the LET of radiation. High linear energy transfer radiation is more deleterious.

Nonetheless, NFL players lived longer than the average male. This is expected for folks who undergo as much physical conditioning as football players do. Even nuclear workers are in better physical shape than the average person. There are lots of people who couldn't get hired at a nuclear plant due to underlying physical problems. And so, studies which compare nuclear workers to the general public suffer from the "healthy worker effect". (Note the effect discussed in that last link dealt with gas workers exposed to carbonized coal...again, it's not just a nuclear thing).

The logic underpinning LNT is used throughout medicine and across many occupations.